The present invention relates to a process for the production of calcium silicate stones as well as an apparatus for the production of stone blocks, especially the production of stone blocks useful in construction building walls.
Calcium silicate stones having densified structures, e.g., sandy limestones, are customarily produced by preparing a mixture of quartz sand, lime and water, the lime thereafter becoming slaked with the water, thereby producing a crude mixture having an essentially dry, almost dusty to slightly soil-moist consistency. Such a crude mixture, when subjected to high pressure on the order of magnitude of more than 15 m.kg/sec.sup.2 /mm.sup.2, can be compacted in a compacting apparatus to form stone blanks. As a result of this compacting, physical bonding forces arise in the stone blanks which, because of the high pressure, are sufficient to allow the blanks to be removed from the mold without damage and thereafter to be transported to an autoclave in which steam curing will take place. The steam curing will result in the development of chemical bonding forces, i.e., due to the formation of calcium silicate hydroxide bridges. However, the use of such high pressures for the production of the stone blanks is disadvantageous, not only because of the apparatus which is required but because the produced stone blanks will have a high fragment bulk density and a low heat damping capacity. In addition, the high fragment bulk density means that the stone blanks cannot be made too large since they will be too heavy for the bricklayers to handle during bricklaying.
According to U.S. Pat. No. 4,229,393, the fragment bulk density of stone blanks can be reduced and the heat damping characteristics increased if cement in a quantity of at least 1% by weight, as well as foam or pore formers, are added to the customary crude mixture of sandy limestone and subsequent compaction pressures of significantly lower than 15 m.kg/sec.sup.2 /mm.sup.2 are used. The addition of cement provides chemical binding forces which partially replaces the physical bonding forces needed to achieve a sufficient strength in the stone blanks since strength-building reactions of the cement are allowed to start prior to the molding of the stone blank. In addition, the fragment bulk density will be considerably reduced by use of a reduced compacting pressure and it is then possible to add lightweight aggregates which further improve the heat damping characteristics of the stone blanks. Stones are produced which have a pattern of holes, a high number of the holes being separated from one another by bridges. These bridges provide a favorable effect on the heat damping characteristics of the stone blanks and moreover will considerably reduce the total weight of the blanks. The strengths of the bridges, however, may not be reduced to the lowest desireable level because to achieve such desired low bridge strengths the bridges must be developed perfectly during formation of the blank. Moreover, the process is difficult to accomplish whenever an intermediate storage of the crude mixture is required prior to the commencement of the strength-creating reactions of the cement. Moreover, the processing of the crude mixture is problematic per se whenever intermediate storage is necessary, and this is especially so with breakdowns in the subsequently utilized elements of the apparatus.